Tank of a low temperature liquefied gas tanker ship

ABSTRACT

A tank of a low temperature liquefied gas tanker ship comprising a lower tank portion formed as a membranous vessel provided at the inside of a rigid hull with interposition of a compression resistant heat insulating layer and an upper tank portion having a rigid structure and fluid-tightly connected to an upper central portion of said lower tank portion, whereby the entire tank structure is favorably supported by the rigid upper tank portion being mounted to the deck of the ship, and because of a smaller horizontal cross-sectional area of the upper tank portion as compared with that of the lower tank portion, the free surface of the liquid loaded in the tank is reduced, especially when partition walls are provided in the upper tank portion, thereby improving the stability of the ship.

ate States atent 1191 Yamamoto 1 1 Dec. 3, 1974 [541 TANK OF A LOW TEMPERATURE 3,315,628 4/1967 Gorman et al. 220/9 LG x LIQUEFIED GAS TANKER SHIP 3,465,528 /1969 Usab 61/5 3,613,932 10/1971 Yamamoto 114/74A x [75] Inventor: Kat suro Yamamoto, Tokyo, Japan [73] Assignee: Bridgestone Liquefied Gas Company, Ltd., Tokyo, Japan [22] Filed: Apr. 18, 1973 [21] App]. No.: 352,312

[30] 7 Foreign Application Priority Data Apr. 21, 1972 Japan 4740093 [52] U.S. Cl 1 14/74 A, 220/9 LG [51] Int. Cl B63b 25/16 [58] Field of Search 114/74 R, 74 A, 75; 220/9 LG, 9 A, 15; 61/5; 62/45, 55

[56] References .Cited UNITED STATES PATENTS 142,842 9/1873 Demartini et al 1 14/75 2,939,294 6/1960 Gorrnory ll4/74 A 2,994,452 3/1961 Morrison 220/9 LG 3,030,780 4/1962 Loveday r 220/9 LG 3,270,700 9/1966 Kohn et a1... 114/74 A 3,310,016 3/1967 Lopker .l 114/75 Primary ExaminerLloyd L. King Assistant Examiner-Randolph A. Reese Attorney, Agent, or FirmStewart and Kolasch, Ltd;

[5 7] ABSTRACT upper tank portion being mounted to the deck of the ship, and because of a smaller horizontal crosssectional area of the upper tank portion as compared with that of the lower tank portion, the free surface of the liquid loaded in the tank is reduced, especially when partition walls are provided in the upper tank portion, thereby improving the stability of the ship.

10 Claims, 5 Drawing Figures PATENTEL {15C 3 I974 FIG.

FIG.

TANK OF A LOW TEMPERATURE LIQUEFIED GAS TANKER SHIP BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a tank of tanker ships for transporting low temperature liquefied gases such as methane, propane, etc., which are in a gaseous state at normal temperature and can be liquefied by being cooled down under atmospheric pressure.

2. Description of the Prior Art Conventionally, as the tanks for the abovementioned purpose there are known tanks of a selfstanding type and of a membrane type. The tank of a membrane type comprises an inner membranous vessel formed of a thin metal plate and provided at the inside of a rigid hull with interposition of a compression resistant heat insulating layer, wherein the inner vessel is adapted to be flexibly deformed due to the internal pressure of the tank to come in close contact with the inner surface of the heat insulating layer so as to transmit the internal pressure to the hull by way of the heat insulating layer thereby to support the load of the tank by the hull. The tank of a membrane type havingthe structure as mentioned above has various advantages as compared with the tanks of a self-standing type. For example, the tank of a membrane type requires a less amount of an expensive material for forming the inner vessel which comes in direct contact with the low temperature liquefied gases, and furthermore, since the inner membranous vessel is easily formed to have a marginal slack as it is constructed at normal temperature that is to compensate a contraction in a low temperature operating condition, the tank is relieved from being subject to a severe stress condition in a low temperature operating condition.

On the other hand, however, the tank of a membrane type has a drawback that it is very difficult to provide partition walls within the tank. In case of a tank provided in a ship, it is important in view of the stability of the ship to divide the inside space of the tank into relatively small compartments in order to suppress swaying or oscillation of the liquid loaded in the tank. When the partition walls are not provided, a number of tanks of a small capacity must be provided, whereby there are encountered economical drawbacks such that the costs of material as well as construction are increased and the'effective space in the ship is very much reduced. Since the partition walls must withstand the shocks applied by the swaying or oscillation of the liquid contained in the tank, the partition walls can not, in case of a tank of a membrane type, be connected to the flexible inner vessel to be supported thereby, but must be directly supported by the hull or a rigid outer vessel. However, since the partition walls are cooled down to a very low temperature due to contact with the low temperature liquefied gases contained in the tank, while the hull or the rigid outer vessel is isolated from the low temperature by the heating insulating layer, there occurs a large temperature difference between the two, and therefore, it is not favorable in view of stress concentration to support such partition walls firmly by the rigid hull. Therefore, it is very difficult to provide partition walls in a tank of a membrane type.

Furthermore, since a tank of a membrane type can not stand by itself in a normal temperature unloaded condition, and especially there is a danger that a roof portion of the inner membranous vessel falls down due to itsown gravity, the roof portion of the inner membranous vessel is usually formed of a relatively thick plate or is adapted to be supported by proper suspension means. However, since the inner vessel is subject to complicated deformations according to the changes of conditions such as from a normal temperature unloaded condition to a low temperature loaded condition by way of a low temperature unloaded condition, it is not favorable in view of stress concentration to apply any restriction to the inner vessel which will prevent the above-mentioned deformations.

A conventional tank of a membrane type is usually provided at its central portion of its roof portion with a trunk of a rigid structure for introducing gas pipes, level gauge, pump and other equipments therethrough into and out of the inner vessel. However, since the trunk is very small as compared with the entire body of the tank, the space in the trunk is too small to effectively contribute to increasing the tank capacity so as to obtain as a large tank capacity as possible.

SUMMARY OF THE INVENTION in a membranous vessel and in addition to provide an increased tank capacity.

Another object of this invention is to provide a tank wherein the roof portion of the membranous vessel as well as pipes and other equipments to be introduced into and out of the tank can be firmly supported.

The above-mentioned objects are accomplished, ac-

cording to this invention, by a tank of a low temperature liquefied gas tanker ship comprising a lower tank portion formed as a membranous vessel provided at the inside of a rigid hull with interposition of a compression resistant heat insulating layer and an upper tank portion having a rigid structure and fluid-tightly connected to an upper central portion of said lower tank portion, said upper tank portion being adapted to be passing through an opening of a deck and to be flexibly mounted at the peripheral portion of said opening, the outer surface of said upper tank being covered with a heat insulating layer.

As described above, the tank of a low temperature liquefied gas tanker ship according to this invention is composed of the upper and lower tank portions having different structures, respectively, wherein the lower tank portion occupying a substantial portion of the tank capacity is formed as a tank of a membrane type which is less expensive and operates more favorably than a tank of a rigid and self-standing type. On the other hand, by the upper tank portion of a rigid structure being connected to the upper central portion of the lower membranous tank portion and extended upward beyond the level of the deck, it is accomplished to effectively suspend the lower membranous tank portion as well as to increase the capacity of the tank. An expansion or contraction of the upper tank portion due to temperature changes is allowed with no trouble by the flexible mounting of the upper tank portion at the peripheral portion of the opening of the deck by means of loose-bolts, etc.

Since the upper tank portion connected at the upper central portion of the lower tank portion has a substantially smaller horizontal cross section as compared with that of the lower tank portion, when the tank has been fully loaded with low temperature liquefied gases, the free surface of the liquid contained in the tank is sub stantially reduced thereby improving the stability of the ship.

According to another feature of this invention, the roof portion of the lower membranous tank portion, especially the portion located around a central opening for connection with the upper tank portion is supported by flange-like means extending horizontally from the lower end peripheral portion of the upper tank.

Generally, in case of a tank of a membrane type including an inner membranous vessel provided at the inside of a rigid outer vessel with interposition of a heat insulating layer, it is necessary to provide special means for holding the inner membranous vessel in its standing shape in a normal temperature unloaded condition. In the tank according to this invention, the roof portion of the lower membranous tank located around the central opening is effectively supported by utilizing the upper tank portion of a rigid structure in the abovementioned manner that the flange-like suspension means are extended from the lower end peripheral portion of the upper tank portion, whereby the lower membranous tank is always held in its standing shape with no danger of falling down due to its own gravity even in a normal temperature unloaded condition.

According to still another feature of this invention, the upper tank portion may be provided with partition walls to suppress oscillations of the surface region of the liquid contained in the tank.

As mentioned above, it is very difficult to firmly mount partition walls in a membranous tank. However, since the tank according to this invention is provided with the upper rigid tank portion in which the liquid loaded in the tank is usually located, partition walls can be very easily mounted at the rigid tank portion in the most effective manner. In other words, by providing the partition walls in the upper tank portion where the free surface of the liquid is substantially reduced, the effect of the partition walls for suppressing oscillations of the loaded liquid is very much increased thereby highly improving the stability of the ship.

According to still another feature of this invention, the rigid upper tank is adapted to carry supporting means for supporting pipes and other means to be introduced into and out of the tank through the roof portion of the upper tank.

In the conventional low temperature liquefied gas tanker ships equipped with tanks of a membrane type, the pipes and other equipments to be introduced into and out of the tank have been directly mounted to the hull structure, requiring a heat insulating structure at a mounting portion. However, according to the abovementioned feature of this invention, the pipes and other equipments can be easily supported by utilizing the rigid structure of the upper tank portion with no requirement of interposition of heat insulating structures, whereby firmer mounting of the pipes and other equipments is obtained.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF ,THE PREFERRED EMBODIMENTS In' the following, this invention will be described in more detail of some preferred embodiments with reference to the accompanying drawing.

FIG. 1 shows in a perspective view a bare tank body of the tank of a low temperature liquefied gas tanker ship according to this invention, wherein reference numeral 1 generally designates a lower membranous tank portion formed of a thin plate of a low temperature resisting material such as aluminuium, stainless steel, nickel steel, etc., said lower tank portion having flat wall portions la, cylindrical edge portions lb and spherical corner portions 10.

Above the lower tank portion 1, and actually in a fluid-tight connection with an opening formed at a central portion of a roof portion la of the lower tank, there is provided an upper tank portion 2 of a rigid structure formed of relatively thick plate of a low temperature resisting material such as aluminium, stainless steel, nickel steel, etc.

Along side walls 2a of the upper tank 2, there is mounted a flange 3, and under the flange 3 and at a central portion of each side wall 2a, there are provided keys 4. A roof portion 2a of the upper tank 2 is provided with a manhole 5 for the inspection of the inside of the tank as well as formed with openings 6 for introducing liquid and gas pipes, pumps, level gauge and other equipments into and out of the tank.

' FIG. 2 is a cross-sectional view of a tanker ship in which the tank structure shown in FIG. 1 is mounted. The ship includes dual-walled hull 7 of a rigid structure, and at the inside of the hull with interposition of a compression resistant heat insulating layer 8, there is mounted the lower tank portion 1 of a membrane structure, while the upper tank portion 2 of a rigid structure is protruded upward through an opening formed at a deck 9 of the hull. As shown in more detail in FIG. 3, the flange 3.0f the upper tank 2 is loosely mounted to a rim member 11 provided along the periphery of the opening formed "at the deck 9 by means of loose-bolts 12, and between the flange 3 and the rim member 11 is provided a hard heat insulating material 10. Horizontal movement of flange 3 relative to the rim member 11 is restricted by a cooperation of the key 4 provided at the underside of the flange and key restricting members 13 provided at the rim member 11, wherein the key restricting members 13 are adapted to hold the key 4 from the opposite sides thereof by way of a hard heat insulating material 10'.

As shown in FIG. 2, flange-like supporting means 14 are extended horizontally outwardly from the lower end portion of the upper tank 2 in a manner to support the roof portion of the lower tank 1 located around the periphery of the upper opening thereof. Pipes l6 and other equipments (not shown) suspended downward into the tank through the roof of the upper tank 2 are supported by supporting members mounted to the wall portion of the upper tank 2. In the drawing, reference numeral 17 designates a heat insulating layer covering the outer surface of the upper tank 2, said heat insulating layer being in turn covered with a thin plate 17a such as steel plate to be protected from the invasion of humidity thereinto.

In a normal temperature unloaded condition or a condition as constructed, the lower tank 1 is adapted to be in a condition as urged toward the inside thereof by the heat insulating layer 8 so that the peripheral length of the lower tank 1 is made larger than that of the inner surface of the heat insulating layer 8. In more detail, the lower tank 1 is adapted to have a marginal slack to compensate a contraction thereof in a low temperature operating condition, such a marginal slack being usually absorbed by deformations of the cylindrical edge portions 1b and the spherical corner portions 1c as well as inward bulging of the flat portions 1a and 1a in a normal temperature unloaded condition.

In a low temperature loaded condition when the lower tank 1 is loaded with low temperature liquefied gases and is subject to an internal pressure exerted by the liquefied gases loaded therein, the lower membranous tank contracts to have deformations of the edge and corner portions as well as the bulging of the flat wall portions disappear, while it is expanded by the internal pressure applied by the low temperature liquefied gases loaded therein and comes in close contact with the inner surface of the heat insulating layer 8 to be finally supported by the hull 7 by way of the heat insulating layer 8. Therefore, the lower membranous tank 1 is subject to no substantial stress except at the edge and corner portions Ib and 10, where the membrane forming the tank is subject to only a simple hoop stress.

It is very difficult, as mentioned above, to provide partition walls in a membranous tank such as the lower tank 1. However, in case of the tank according to this invention, when the tank is fully loaded with low temperature liquefied gases, the free surface of the liquid in the tank is positioned within the region of the upper tank 2. Therefore, by providing partition walls in the upper tank 2 having the rigid structure, the swaying or oscillation of the free surface of the liquid is more favorably suppressed.

FIG. 5 shows another embodiment of this invention, wherein partition walls 18 are provided in the upper tank portion 2. In this case the opening provided at the roof portion of the lower tank 1 is extended to be positioned relatively closely to the outer edge portions of the lower tank so that the remaining roof portion of the lower tank forms a relatively narrow band region positioned around the opening. In this case, the flange-like supporting means 14 as shown in FIG. 2 are not required, and in addition, the horizontally cross-sectional area of the upper tank 2 is very much increased. Therefore, a number of partition walls 18 are provided as extended from the roof portion 2a of the upper tank 2 to suppress the swaying or oscillation of the free surface of the liquid contained in the tank. As a modification, the partition walls 18 may be replaced by a plate having a number of perforations and adapted to be positioned horizontally and adjacently to the free surface of the liquid contained in the tank. By such a perforated plate, the swaying or oscillation of the free surface of the liquid can be also effectively suppressed.

In the embodiment shown in FIG. 5, the pipe 16 is suspended by the supporting means 15 in the form of a wire from the lower end portion of the upper tank 2, and'at the portion where the pipe 16 penetrates the roof portion 2a of the upper tank 2, fluid-tightness and allowance of a relative movement of the pipe 16 with respect to the roof portion 2a are attained by a provision of a bellows 19.

In FIG. 5, reference numeral 20 shows a member mounted to the partition walls for restricting the swaying of the pipe 16. In FIG. 5, the portions corresponding to those shown in FIG. 2 are designated by the same reference numerals.

In either embodiment shown in FIGS. 2 or 5, a space large enough to contain evaporated gases can be provided above the free surface of the liquid within the region of the upper tank 2, and furthermore, by the provision of the upper tank 2, the overall capacity of the tank is very effectively increased.

From the foregoing, it will be appreciated that the tank according to this inventionpreserves the merit of the tank of a membrane type, and in addition has an effect of suppressing the swaying or oscillation of the free surface of the liquid contained in the tank thereby improving the stability of the ship, and still in addition has an advantage of providing an increased capacity of the tank. It is also an additional advantage of this invention that the pipes and other equipments to be introduced into and out of the tank are firmly supported by the upper tank portion having the rigid structure.

I claim:

l. A low temperature liquefied gas tank for use in conjunction with a tanker ship which comprises a lower tank portion formed of a membranous member and provided at the inside of a rigid hull with the interposition of a compression resistant heat-insulating layer disposed therebetween and an upper tank portion formed of a rigid structure and connected in a fluid tight manner to the upper central portion of said lower tank portion, said upper tank portion extending through and protruding above an opening provided in a deck, said upper tank portion having an internal space large enough to provide a safe buffer space even when the liquefied gases have been loaded to a level extending substantially into said upper tank portion, and means for enabling said upper tank portion to be flexibly carried by the deck so as to be expandable in the horizontal direction. 7

2. A tank according to claim I, wherein a portion of said lower tank portion located adjacent a lower end portion of said upper tank portion is supported by supporting means extending substantially horizontally from said lower end portion of said upper tank portion.

3. A tank according to claim I, wherein said upper tank portion is provided with at least 1 partition wall adapted to divide the free surface of a liquid loaded in the tank.

4. A tank according to claim 1, wherein said upper tank portion is mounted with supporting means for supporting pipes and other equipmentto be introduced into and out of the tank.

5. A tank according to claim 1, wherein said upper tank portion is provided with a perforated plate positioned substantially horizontally therein.

6. A tank according to claim 1, wherein said flexible mounting between said upper tank portion and said deck is restrictively guided by cooperation of keys mounted to said upper tank portion and key restricting members mounted to said deck, both being engaged with each other with the interposition of a hard heat insulating material.

7. A low temperature liquefied gas tank adapted for use in conjunction with a tanker ship for housing a liquid which comprises a lower tank portion formed of a membranous member and disposed below the free surface of the liquid and an upper tank portion formed of a rigid structure and adapted to house the free surface of the liquid said upper tank portion being connected in a fluid tight manner to the lower tank portion, said upper tank portion being small enough to provide a much smaller free surface area, relative to the area of the lower tank portion in order to reduce the shocks due to the oscillation of the free surface of the liquid, but said upper tank portion being largeenough to substantially increase the overall tank capacity and function as a buffer space to absorb a change in the volume of the liquid phase due to a change in the temperature thereof.

8. The lower temperature liquefied gas tank of claim 7, wherein means are provided for flexibily mounting the upper tank portion at its periphery so as to be expandable in the horizontal direction, said flexible mounting means providing for expansion or contraction of the upper tank due to temperature changes.

9. The low temperature liquefied gas tank of claim 7, wherein at least one partition wall is provided in the upper tank portion to divide the free surface area of the liquid disposed therein, to further suppress the swaying or oscillation of the free surface of the liquid contained in said tank.

10. The low temperature liquefied gas tank of claim 7, wherein the upper tank portion is only slightly smaller than the lower tank portion and at least one partition wall is provided in said upper tank portion to divide the free surface of the liquid disposed therein. 

1. A low temperature liquefied gas tank for use in conjunction with a tanker ship which comprises a lower tank portion formed of a membranous member and provided at the inside of a rigid hull with the interposition of a compression resistant heat-insulating layer disposed therebetween and an upper tank portion formed of a rigid structure and connected in a fluid tight manner to the upper central portion of said lower tank portion, said upper tank portion extending through and protruding above an opening provided in a deck, said upper tank portion having an internal space large enough to provide a safe buffer space even when the liquefied gases have been loaded to a level extending substantially into said upper tank portion, and means for enabling said upper tank portion to be flexibly carried by the deck so as to be expandable in the horizontal direction.
 2. A tank according to claim 1, wherein a portion of said lower tank portion located adjacent a lower end portion of said upper tank portion is supported by supporting means extending substantially horizontally from said lower end portion of said upper tank portion.
 3. A tank according to claim 1, wherein said upper tank portion is provided with at least 1 partition wall adapted to divide the free surface of a liquid loaded in the tank.
 4. A tank according to claim 1, wherein said upper tank portion is mounted with supporting means for supporting pipes and other equipment to be introduced into and out of the tank.
 5. A tank according to claim 1, wherein said upper tank portion is provided with a perforated plate positioned substantially horizontally therein.
 6. A tank according to claim 1, wherein said flexible mounting between said upper tank portion and said deck is restrictively guided by cooperation of keys mounted to said upper tank portion and key restricting members mounted to said deck, both being engaged with each other with the interposition of a hard heat insulating material.
 7. A low temperature liquefied gas tank adapted for use in conjunction with a tanker ship for housing a liquid which comprises a lower tank portion formed of a membranous member and disposed below the free surface of the liquid and an upper tank portion formed of a rigid structure and adapted to house the free surface of the liquid said upper tank portion being connected in a fluid tight manner to the lower tank portion, said upper tank portion being small enough to provide a much smaller free surface area, relative to the area of the lower tank portion in order to reduce the shocks due to the oscillation of the free surface of the liquid, but said upper tank portion being large enough to substantially increase the overall tank capacity and function as a buffer space to absorb a change in the volume of the liquid phase due to a change in the temperature thereof.
 8. The lower temperature liquefied gas tank of claim 7, wherein means are provided for flexibily mounting the upper tank portion at its periphery so as to be expandable in the horizontal direction, said flexible mounting means providing for expansion or contraction of the upper tank due to temperature changes.
 9. The low temperature liquefied gas tank of claim 7, wherein at least one partition wall is provided in the upper tank portion to divide the free surface area of the liquid disposed therein, to further suppress the swaying or oscillation of the free surface of the liquid contained in said tank.
 10. The low temperature liquefied gas tank of claim 7, wherein the upper tank portion is only slightly smaller than the lower tank portion and at least one partition wall is provided in said upper tank portion to Divide the free surface of the liquid disposed therein. 